Methods have conventionally been proposed for increasing the numerical aperture (NA) of an objective lens in order to increase the information recording density of optical recording media, such as optical disks, optical cards, etc. One such method is to dispose an SIL (solid immersion lens) between the optical recording medium and the objective lens. However, the addition of an SIL to an optical pickup increases the weight of the read/write head, which must be controlled to move at high speed. To avoid this problem, a method using an SIM (solid immersion mirror) has been proposed (ODF '98, Tokyo, Jun. 16, 1998, “Objective Lenses for DVD & Near Field Optical Disk Pick-up”). The SIM is a catadioptric system in which the luminous flux incident on a central portion is reflected at a peripheral portion.
Since the SIM is formed of surfaces defined by a discontinuous expression, the decentration error of each surface is large and its configuration is complicated. Therefore, it is extremely difficult to form the SIM by glass molding using a high-refractive-index glass material. When the SIM is used in a case where uniform light is incident, while the numerical aperture can be increased (the angle with respect to the light spot can be increased), a sufficient light quantity cannot be obtained because only a central part of the luminous flux can be used.